Isotopes of calcium (20Ca)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
40Ca 96.9% stable
41Ca trace 9.94×104 y ε 41K
42Ca 0.647% stable
43Ca 0.135% stable
44Ca 2.09% stable
45Ca synth 163 d β− 45Sc
46Ca 0.004% stable
47Ca synth 4.5 d β− 47Sc
48Ca 0.187% 6.4×1019 y β−β− 48Ti
Standard atomic weight Ar°(Ca)
  • 40.078±0.004
  • 40.078±0.004 (abridged)[2][3]

Calcium (20Ca) has 26 known isotopes, ranging from 35Ca to 60Ca. There are five stable isotopes (40Ca, 42Ca, 43Ca, 44Ca and 46Ca), plus one isotope (48Ca) with such a long half-life that for all practical purposes it can be considered stable. The most abundant isotope, 40Ca, as well as the rare 46Ca, are theoretically unstable on energetic grounds, but their decay has not been observed. Calcium also has a cosmogenic isotope, radioactive 41Ca, which has a half-life of 99,400 years. Unlike cosmogenic isotopes that are produced in the atmosphere, 41Ca is produced by neutron activation of 40Ca. Most of its production is in the upper metre of the soil column, where the cosmogenic neutron flux is still sufficiently strong. 41Ca has received much attention in stellar studies because it decays to 41K, a critical indicator of solar system anomalies. The most stable artificial radioisotopes are 45Ca with a half-life of 163 days and 47Ca with a half-life of 4.5 days. All other calcium isotopes have half-lives measured in minutes or less.[4]

40Ca comprises about 97% of naturally occurring calcium. 40Ca is also one of the daughter products of 40K decay, along with 40Ar. While K–Ar dating has been used extensively in the geological sciences, the prevalence of 40Ca in nature has impeded its use in dating. Techniques using mass spectrometry and a double spike isotope dilution have been used for K–Ca age dating.

List of isotopes

Around 2 g of calcium-48
Nuclide
 Z N Isotopic mass (Da)[5]
[n 1]		 Half-life[1]
[n 2]		 Decay
mode[1]
[n 3]		 Daughter
isotope
[n 4]		 Spin and
parity[1]
[n 5][n 6]		 Natural abundance (mole fraction)
Normal proportion[1] Range of variation
35Ca 20 15 35.00557(22)# 25.7(2) ms β+, p (95.8%) 34Ar 1/2+#
β+, 2p (4.2%) 33Cl
β+ (rare) 35K
36Ca 20 16 35.993074(43) 100.9(13) ms β+, p (51.2%) 35Ar 0+
β+ (48.8%) 36K
37Ca 20 17 36.98589785(68) 181.0(9) ms β+, p (76.8%) 36Ar 3/2+
β+ (23.2%) 37K
38Ca 20 18 37.97631922(21) 443.70(25) ms β+ 38K 0+
39Ca 20 19 38.97071081(64) 860.3(8) ms β+ 39K 3/2+
40Ca[n 7] 20 20 39.962590850(22) Observationally stable[n 8] 0+ 0.9694(16) 0.96933–0.96947
41Ca 20 21 40.96227791(15) 9.94(15)×104 y EC 41K 7/2− Trace[n 9]
42Ca 20 22 41.95861778(16) Stable 0+ 0.00647(23) 0.00646–0.00648
43Ca 20 23 42.95876638(24) Stable 7/2− 0.00135(10) 0.00135–0.00135
44Ca 20 24 43.95548149(35) Stable 0+ 0.0209(11) 0.02082–0.02092
45Ca 20 25 44.95618627(39) 162.61(9) d β− 45Sc 7/2−
46Ca 20 26 45.9536877(24) Observationally stable[n 10] 0+ 4×10−5 4×10−5–4×10−5
47Ca 20 27 46.9545411(24) 4.536(3) d β− 47Sc 7/2−
48Ca[n 11][n 12] 20 28 47.952522654(18) 5.6(10)×1019 yβ−β−[n 13][n 14] 48Ti 0+ 0.00187(21) 0.00186–0.00188
49Ca 20 29 48.95566263(19) 8.718(6) min β− 49Sc 3/2−
50Ca 20 30 49.9574992(17) 13.45(5) s β− 50Sc 0+
51Ca 20 31 50.96099566(56) 10.0(8) s β− 51Sc 3/2−
β−, n? 50Sc
52Ca 20 32 51.96321365(72) 4.6(3) s β− (>98%) 52Sc 0+
β−, n (<2%) 51Sc
53Ca 20 33 52.968451(47) 461(90) ms β− (60%) 53Sc 1/2−#
β−, n (40%) 52Sc
54Ca 20 34 53.972989(52) 90(6) ms β− 54Sc 0+
β−, n? 53Sc
β−, 2n? 52Sc
55Ca 20 35 54.97998(17) 22(2) ms β− 55Sc 5/2−#
β−, n? 54Sc
β−, 2n? 53Sc
56Ca 20 36 55.98550(27) 11(2) ms β− 56Sc 0+
β−, n? 55Sc
β−, 2n? 54Sc
57Ca 20 37 56.99296(43)# 8# ms [>620 ns] β−? 57Sc 5/2−#
β−, n? 56Sc
β−, 2n? 55Sc
58Ca 20 38 57.99836(54)# 4# ms [>620 ns] β−? 58Sc 0+
β−, n? 57Sc
β−, 2n? 56Sc
59Ca 20 39 59.00624(64)# 5# ms [>400 ns] β−? 59Sc 5/2−#
β−, n? 58Sc
β−, 2n? 57Sc
60Ca 20 40 60.01181(75)# 2# ms [>400 ns] β−? 60Sc 0+
β−, n? 59Sc
β−, 2n? 58Sc
This table header & footer:
  1. ↑ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  2. ↑ Bold half-life – nearly stable, half-life longer than age of universe.
  3. ↑ Modes of decay:
    EC:Electron capture
    n:Neutron emission
    p:Proton emission
  4. ↑ Bold symbol as daughter – Daughter product is stable.
  5. ↑ ( ) spin value – Indicates spin with weak assignment arguments.
  6. ↑ # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  7. ↑ Heaviest observationally stable nuclide with equal numbers of protons and neutrons
  8. ↑ Believed to undergo double electron capture to 40Ar with a half-life no less than 9.9×1021 y
  9. ↑ Cosmogenic nuclide
  10. ↑ Believed to undergo β−β− decay to 46Ti
  11. ↑ Primordial radionuclide
  12. ↑ Believed to be capable of undergoing triple beta decay with very long partial half-life
  13. ↑ Lightest nuclide known to undergo double beta decay
  14. ↑ Theorized to also undergo β− decay to 48Sc with a partial half-life exceeding 1.1+0.8
    −0.6    ×1021 years[6]

Calcium-60

Calcium-60 is the heaviest known isotope as of 2020.[1] First observed in 2018 at Riken alongside 59Ca and seven isotopes of other elements,[7] its existence suggests that there are additional even-N isotopes of calcium up to at least 70Ca, while 59Ca is probably the last bound isotope with odd N.[8] Earlier predictions had estimated the neutron drip line to occur at 60Ca, with 59Ca unbound.[7]

In the neutron-rich region, N = 40 becomes a magic number, so 60Ca was considered early on to be a possibly doubly magic nucleus, as is observed for the 68Ni isotone.[9][10] However, subsequent spectroscopic measurements of the nearby nuclides 56Ca, 58Ca, and 62Ti instead predict that it should lie on the island of inversion known to exist around 64Cr.[10][11]

References

  1. 1 2 3 4 5 6 Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
  2. ↑ "Standard Atomic Weights: Calcium". CIAAW. 1983.
  3. ↑ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; et al. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
  4. ↑ Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017). "The NUBASE2016 evaluation of nuclear properties" (PDF). Chinese Physics C. 41 (3): 030001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.
  5. ↑ Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.
  6. ↑ Aunola, M.; Suhonen, J.; Siiskonen, T. (1999). "Shell-model study of the highly forbidden beta decay 48Ca → 48Sc". EPL. 46 (5): 577. Bibcode:1999EL.....46..577A. doi:10.1209/epl/i1999-00301-2. S2CID 250836275.
  7. 1 2 Tarasov, O. B.; Ahn, D. S.; Bazin, D.; et al. (11 July 2018). "Discovery of 60Ca and Implications For the Stability of 70Ca". Physical Review Letters. 121 (2). doi:10.1103/PhysRevLett.121.022501.
  8. ↑ Neufcourt, Léo; Cao, Yuchen; Nazarewicz, Witold; et al. (14 February 2019). "Neutron Drip Line in the Ca Region from Bayesian Model Averaging". Physical Review Letters. 122 (6). arXiv:1901.07632. doi:10.1103/PhysRevLett.122.062502.
  9. ↑ Gade, A.; Janssens, R. V. F.; Weisshaar, D.; et al. (21 March 2014). "Nuclear Structure Towards N = 40 60Ca: In-Beam γ -Ray Spectroscopy of 58, 60Ti". Physical Review Letters. 112 (11). arXiv:1402.5944. doi:10.1103/PhysRevLett.112.112503.
  10. 1 2 Cortés, M.L.; Rodriguez, W.; Doornenbal, P.; et al. (January 2020). "Shell evolution of N = 40 isotones towards 60Ca: First spectroscopy of 62Ti". Physics Letters B. 800: 135071. arXiv:1912.07887. doi:10.1016/j.physletb.2019.135071.
  11. ↑ Chen, S.; Browne, F.; Doornenbal, P.; et al. (August 2023). "Level structures of 56, 58Ca cast doubt on a doubly magic 60Ca". Physics Letters B. 843: 138025. arXiv:2307.07077. doi:10.1016/j.physletb.2023.138025.

Further reading

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